This invention related to the production of nuclear fuel, and more particularly to the production of plutonium-containing mixed oxide nuclear fuel (hereinafter referred to as "MOX fuel"), such as mixed plutonium oxide and uranium oxide nuclear fuel.
The reactivity of MOX fuel assemblies over their lifetime in a nuclear reactor can be affected by plutonium isotopic variations if no special measures are taken to counter the effect of the variations. Plutonium isotopic variations can also cause local hot spots in MOX fuel assemblies which can increase within-assembly peaking factors should the highest rated fuel rod contain plutonium with a higher than specified fissile plutonium fraction. To alleviate these problems the current practice by MOX fuel manufacturers is either to homogenise all the Pu(NO.sub.3) .sub.4 required for an entire reactor reload of MOX fuel assemblies or, alternatively, to use a `mix and match ` approach of blending Pu(NO.sub.3).sub.4 from various separate batches in order to meet the specified plutonium isotopic composition.